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Diabetes in cats and dogs

Diabetes mellitus strikes 1 in 400 cats and a similar number of dogs. Symptoms in dogs and cats are similar to those in humans. Generally, most dogs and about half of cats experience type-1 (insulin-dependent) diabetes, rather than the type-2 that's now becoming common in obese humans. The condition is definitely treatable, and need not shorten the animal's life span or life quality. Untreated, the condition leads to blindness in dogs, increasingly weak legs in cats, and eventually malnutrition, ketoacidosis and/or dehydration, and death.


Cats and dogs will generally show a gradual onset of the disease over a few weeks, and it may escape notice for a while. The condition is unusual in animals less than 7 years old. The first obvious symptoms are a sudden weight loss or gain, accompanied by excessive drinking and urination. Appetite is suddenly either ravenous (up to 3 times normal) or absent. In dogs, the next symptom is vision problems and cataracts, while in cats the back legs will become weak and the gait may become stilted or wobbly. A quick test at this point can be done using keto-strips (the same as used on the Atkins diet) or keto/glucose strips, with your pet. If the keto/glucose strips show glucose in the urine, diabetes is indicated. If either strip shows ketones in the urine, the pet should be brought to an emergency clinic right away.

Watch for noticeable thinning of the skin and apparent fragility -- these are also serious and indicate that the pet is consuming all its body fat. Dehydration is also common by this point, and death can follow quickly.


First, get a diagnosis from your veterinarian immediately. Diabetes can be treated but is life-threatening if left alone. Early diagnosis and treatment can help, not only in preventing nerve damage, but in some cases can even lead to a complete remission.


Diet is a critical component of treatment, and is in many cases effective on its own. For example, a recent mini-study showed that many diabetic cats stopped needing insulin after changing to a low-carbohydrate diet. The rationale is that a low-carb diet reduces the amount of insulin needed and keeps the variation in blood sugar low and easier to predict. Also, fats and proteins are turned into blood glucose much more slowly and evenly than carbohydrates, reducing blood-sugar highs right after mealtimes.

Some veterinarians recommend a high-fiber diet with medium-level carbohydrates instead, but this theory is no longer credited for cats, though it may be for dogs.

It's now becoming clear that lower carbohydrate diets will significantly lower insulin requirements for diabetic cats. Carbohydrate levels are highest in dry cat foods (even the expensive prescription types) so cats are best off usually with a low-carb healthy canned diet.


Oral medications like Glipizide that stimulate the pancreas promoting insulin release, (or in some cases, reduce glucose production) work in some small proportion of cats (Most dogs are Type I diabetics so oral hypoglycemic drugs are usually not prescribed for them), but these drugs may be completely ineffective if the pancreas is not working. Collective experience from the Feline Diabetes Message Board indicates that 4-6 weeks is a maximum trial period for oral medication -- if it's ineffective, the cat is starving, and longer can harm the cat. Don't be reluctant to switch from pills to insulin injections -- the difference in cost and convenience is minor, (many cats are easier to inject than to pill!) and injections are more effective in most cases.

Insulin injections

Humans with Type-1 diabetes are often treated with a "basal plus bolus" method, where a long-acting insulin is injected once or twice daily to provide a "basal" insulin level, then shorter-acting insulin is used just before mealtimes. For cats and dogs a "basal" method is usually employed instead -- a single slow-acting dose, twice daily, attempts to keep the blood sugar within a recommended range for the entire day. In this case it's important for the pet to avoid large meals or vigorous exercise sessions, since both can seriously affect the blood sugar. (Meals may also be timed to coincide with peak insulin activity.) Once-daily doses are not recommended for pets, since insulin metabolizes faster in cats and dogs than in humans; an insulin brand that lasts 24 hours in people may only be good for about 12 in a cat.

Cats and dogs may be treated with animal insulins (pork-based seems to work best in dogs, beef-based in cats), or with human or synthetic insulins. The best choice of insulin brand and type varies between pets and may require some experimentation. One of the popular insulins, Humulin N /Novolin N/ NPH, is reasonable for dogs, but may be a poor choice for cats, since cats' metabolisms run about twice as fast. Until the early 1990's, the most recommended type for pets was beef/pork-derived PZI], but that type was phased out over the 1990's and is now difficult to find in many countries. There are sources in the US and UK, and many vets are now starting to recommend them again for pets.

Two new ultra-slow time-release synthetic insulins are just becoming available in 2004 and 2005 for improving basal stability, generically known as Insulin Detemir ("Levemir") and Insulin Glargine ("Lantus"). A mini-study at the University of Brisbane, Australia has had remarkable results with Insuline Glargine in cats. No studies have yet been performed on pets with Detemir/Levemir, but early anecdotal evidence shows that it is also very effective on cats.

Neuropathy in cats

The weak legs syndrome is a form of neuropathy, in particular caused by damage to the myelin sheath of the peripheral nerves caused by poor circulation and cell starvation. Most common in cats, the back legs become weaker until the cat displays "Plantigrade stance", standing on its hocks instead of on its toes as usual. The cat may also have trouble walking and jumping, and may need to sit down after a few steps. Some recommend a form of vitamin B12 called methylcobalamin to heal the nerve damage. Neuropathy often heals on its own within 1 to 3 months once blood sugar is regulated, but anecdotal evidence points to a higher success rate with these supplements.

Blindness in dogs

Dogs' eyes are highly sensitive to high blood sugar, and will have blurred vision, cataracts, or even total blindness after as little as a few days at blood glucose concentration above 16.7mmol (300 mg/mL). Cataracts may be treated later, but blindness is permanent in some cases. Fortunately, dogs rely more on smell and hearing than on vision, and so may surprise you with how well they get along without their eyes.

Dosage and Regulation

Cats and dogs may in some cases have their mealtimes strictly scheduled and planned to match with injection times. In other cases where the pet free-feeds and normally eats little bits all day or night, it may be best to remain on this schedule and try to use a very slow-acting insulin to keep a constant level of blood glucose. Consult your veterinarian. Note that some veterinarians still use the outdated recommendation of using Humulin "N" or NPH insulin for cats. This insulin is too fast-acting for most cats (though fine for dogs and humans). Cat metabolism runs about twice as fast as human, so Humulin L or U are better insulins to begin with.

The goal at first is to "regulate" the pet's blood glucose, which may take a few weeks or even many months. This process is basically the same as in type-1 diabetic humans. The goal is to keep the blood glucose values in a comfortable range for the pet during the whole day, or most of it.

The recommended method is to Start Low - Go Slow:

  1. Have an initial blood curve taken over 24 hours at the vet and receive an initial dosage recommendation.
  2. The initial dosage will be very conservative (low) (usually between 0.5 and 2.5 units daily, split into 12-hour dosages) and may not affect the pet's symptoms noticeably at first. This is necessary because although high blood sugar can kill within weeks, low blood sugar can kill in minutes. Dosage must be increased gradually and carefully. The usual recommended method is to increase the dose by 1/2 to 1 unit every 7 to 14 days, followed by further glucose testing. Buying an inexpensive blood glucose meter and testing for yourself is essential -- it will save many expensive trips to the vet, avoid dangerous overdoses, and give you a better handle on the pet's ongoing condition. Urine strips are not accurate enough for this.
  3. Your pet is "regulated" when its blood glucose remains within an acceptable range all day, every day. Acceptable varies somewhat between cats, dogs, and vets, but is roughly from 5 to 16.7 mmol/L (90 to 300 mg/mL in the USA) for cats, and between 5 and 14 (90 to 250) for dogs. (The range is wider for diabetic animals than non-diabetic, since shots cannot replicate the accuracy of a working pancreas.) It's important, though, that the glucose level be in the lower half of that range for as much of the day as possible. If you are not doing home glucose testing, some vets recommend that you stop increasing the dosage when the dog or cat is drinking normally, urinating normally, and eating normally, although organ damage may continue in some cases until glucose is below the "Renal Threshold" -- testing urine with keto/glucostix will show when this has been achieved.
  4. Obstacles to regulation:
    • Sometimes your pet will suddenly appear to need less insulin than before. If this happens (their blood sugar will go lower than usual one day), drop the dose immediately and call your vet. If testing just before an injection, and the reading is much lower than expected, it may be wisest to skip that dose and continue retesting every 2-3 hours. If the drop is dramatic and leads to a hypoglycemic episode (see below), the cat's sensativit to insulin may increase dramatically. You should consider dropping their dose after consulting your veterinarian, and raise it only by half to one unit per 5-7 days, as before.
    • Sometimes your pet's blood sugar will suddenly seem much higher than usual. This is not a good time to increase their insulin dosage -- quite the opposite. It often indicates that a low blood sugar condition (or rapid sugar drop) was experienced a few hours before, and a Somogyi rebound is in progress. To be sure, drop the next dose by 15%-50% and take glucose readings every 4 to 8 hours until the glucose levels out. Then wait a few more days for the Somogyi hormones to decrease in the body, and then you can increase again by 0.5-unit steps every 5-7 days. If you experienced this rebound, chances are that your original dose was too high, so you should try to find an ideal dose at a lower point.
    • Chronic overdose masked by Somogyi: A dose that is fractionally too high can easily cause a Somogyi rebound, which can look like a need for more insulin. This condition can continue for days or weeks, and it's very hard on the cat's metabolism. See more on this topic in the Somogyi section below.
    • High-carb cat/dog food: Many commercial foods (especially "Light" foods) are extremely high in cereals and therefore carbohydrates. The extra carbohydrates will keep the cat or dog's blood sugar high, and if you're free-feeding may also make the blood sugar curve over the course of the day unpredictable. In general, canned foods are lower in carbohydrates than dry ones, and canned "kitten" foods lower still. Recent studies show that cats' diabetes can be better regulated and even sometimes cured with a low-carbohydrate diet. This may not apply to dogs. If switching to a lower-carbohydrate food, do it gradually and lower the insulin dosage appropriately, with your vet's help. If your cat is on a special diet for pancreatitis, chronic renal failure, or any other condition, treat that condition first (don't change diet), it is better to control the blood glucose with insulin.
    • Wrong insulin: Different brands and types of insulin have idiosyncratic effects on different cats and dogs. If you've settled on a dose that seems to keep the pet's blood sugar within range at peak effectiveness, but the sugar readings remain dangerously high at shot times, the insulin may not be lasting long enough for your pet, or may not be the best choice. Switching to a slower-acting or a better-tolerated insulin for that pet, and lowering the dose initially to be safe, may be the next step.

Absolute numbers vary between pets, but for general guidelines only, the levels to watch are approximately:





this is an average non-diabetic pet's level, but leaves little margin of safety for a diabetic.



a common minimum safe value for the lowest blood sugar of the day



desired range for diabetics (non-diabetic range is 40-130 but usually unsafe to aim for)



"Renal Threshold" excess glucose from the kidneys spills into the urine, pet begins to show diabetic symptoms. Long term damage to eyes, nerves, and other organs if glucose remains above here too often.



the maximum safe value for the highest blood sugar of the day, in dogs, to avoid short-term eye damage.



the maximum safe value for the highest blood sugar of the day, in cats, to avoid short-term nerve damage.

The regulation process is described in more detail here.

Detecting and avoiding Chronic Somogyi Rebound

It's confusing but true: Too little insulin means pre-shots are too high; too much insulin often also means pre-shots are too high. This effect is often noted by those who test their pets' blood glucose at home.

The reason: Anytime the glucose level drops too far or too fast, the cat or dog will defensively dump glycogen from the liver, as well as hormones epinephrine and cortisol, into the bloodstream. (If these are insufficient, hypoglycemia ensues!) The glycogen raises the blood glucose, the other two make the pet insulin-resistant for a day or two. This phenomenon was first documented by a Dr. Somogyi..

Alternating high and low blood sugar numbers with no apparent logic usually mean repeated Somogyi Rebound. High, flat, unresponsive blood sugar over a period of days is also a typical Chronic Somogyi Rebound sign. This pattern occurs mostly with long-duration insulins given in overdose amounts. Sometimes this high flat curve will be punctuated by sudden drops to very low values, (with possible hypoglycemic events) followed by more high unresponsive numbers.

Even when raising the insulin dose slowly and carefully, it's possible to pass the correct dose and go on to a slight overdose. (A typical case is increasing bidaily dosage from 1 unit to 2, passing a correct dose of 1.5 units.) This may produce a rebound -- a swift jump in blood glucose up from a dangerously low reading, to beyond the previous pre-shot level. The pet may be a bit less responsive to the same dose the next shot, from those other hormones.

According to recent experience on internet diabetes forums, this phenomenon may be less dramatic and more common than usually thought. The term "mini-rebound" is beginning to gain currency. If your insulin dose is just a smidgen high, you may see either nothing at all, or a hypoglycemic episode or a mini-rebound. Some Feline Diabetes Message Board regulars describe mini-rebounds here:

A normal rise will instead be slow and gradual. One way to tell the difference is to take a "curve" (repeated tests every 2 hours) on a weekend and look for the shape of the curve. If the curve is valley-shaped, and gradual, with lowest point in normal glucose ranges (60-130), all is well. Other shapes should arouse suspicion. To check if this is a rebound, the only sure way is to reduce dosage and look for a flatter curve.

Anytime blood glucose numbers seem higher after dosage is raised, consider the possibility of a somogyi rebound.

Hypoglycemic Episode

An acute hypoglycemic episode (very low blood sugar) can happen even if you are careful, since pets' insulin requirements sometimes change without warning. The symptoms are depression/lethargy, confusion/dizziness, loss of excretory/bladder control, vomiting, and then loss of consciousness and/or seizures. As soon as possible, administer honey or corn syrup by rubbing it on the gums (even if unconscious, but not if in seizures), and rush it to the vet. Carry more honey or corn syrup with you on the way and keep rubbing it on the gums, where it can be absorbed -- it could save the pet's life. Every minute without blood sugar causes brain damage. (Some recommend administering syrup anally if the animal is in seizures!)

If the pet has hypoglycemia according to the blood glucose meter, but no symptoms, give treats or food if possible. If they won't eat, administer some honey followed by food or cat treats, and continue to do so until the blood glucose is rising, and the latest insulin shot's peak action is past.

Sometimes a mild hypoglycemic episode will go unnoticed, or leave evidence such as an "accident" where kitty fails to make it to the litterbox. In these cases the blood sugar will probably appear paradoxically high upon the next test hours later, since the pet's body will react to the low blood sugar by stimulating the liver to release stored glycogen. This condition is known as Somogyi rebound (see link above), and requires a lowered insulin dosage for the next few days. The Somogyi rebound may also occur when the pet's blood glucose drops too rapidly, even if it never actually reaches a low reading.

Remission in cats

It is in many cases possible to induce remission (a temporary or permanent freedom from insulin-dependence) in cats. (This appears to be peculiar to cats.) There is little agreement among experts on how this is reliably achieved, but it does happen in 20, 30, or even 40 percent of cats who are properly regulated quickly. Chances of success are highest in the first few months after initial diagnosis. A likely explanation is that a damaged cat's pancreas can sometimes regenerate itself, but continued high blood-sugar is toxic to the pancreas and prevents regeneration. A combination of low-carb healthy diet, well-chosen insulin, and well-chosen dosage plans can in many cases heal a damaged pancreas and allow the cat's blood sugar to be controlled entirely by diet thereafter.